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.save test.js Session saved to:test.js .load test.js var x 10 undefined var y 20 undefined x y 30 var sum undefined console.log(sum) 30 undefined NODE.JS - NPM npm stands for Node Package Manager. npm provides following two main functionalities: Online repositories for node.js packages/modules which are searchable on search.nodejs.org Command line utility to install packages, do version management and dependency management of Node.js packages. npm comes bundled with Node.js installables after v0.6.3 version. To verify the same, open console and type following command and see the result: C:\Nodejs WorkSpace npm --version 2.5.1 Global vs Local installation By default, npm installs any dependency in the local mode. Here local mode refers to the package installation in node modules directory lying in the folder where Node application is present. Locally deployed packages are accessible via require. Globally installed packages/dependencies are stored in user-directory /npm directory. Such dependencies can be used in CLI CommandLineInterface function of any node.js but can not be imported using require in Node application directly. Let's install express, a popular web framework using local installation. C:\Nodejs WorkSpace npm install express express@4.11.2 node modules\express -- merge-descriptors@0.0.2 -- utils-merge@1.0.0 -- methods@1.1.1 -- escape-html@1.0.1 -- fresh@0.2.4 -- cookie@0.1.2 -- range-parser@1.0.2 -- media-typer@0.3.0 -- cookie-signature@1.0.5 -- vary@1.0.0 -- finalhandler@0.3.3 -- parseurl@1.3.0 -- serve-static@1.8.1 -- content-disposition@0.5.0 -- path-to-regexp@0.1.3 -- depd@1.0.0 -- qs@2.3.3 -- debug@2.1.1 (ms@0.6.2) -- send@0.11.1 (destroy@1.0.3, ms@0.7.0, mime@1.2.11) -- on-finished@2.2.0 (ee-first@1.1.0) -- type-is@1.5.7 (mime-types@2.0.9) -- accepts@1.2.3 (negotiator@0.5.0, mime-types@2.0.9) -- etag@1.5.1 (crc@3.2.1) -- proxy-addr@1.0.6 (forwarded@0.1.0, ipaddr.js@0.1.8) Once npm completes the download, you can verify by looking at the content of C:\Nodejs WorkSpace\node modules. Or type the following command:

C:\Nodejs WorkSpace npm ls C:\Nodejs WorkSpace -- express@4.11.2 -- accepts@1.2.3 -- mime-types@2.0.9 -- mime-db@1.7.0 -- negotiator@0.5.0 -- content-disposition@0.5.0 -- cookie@0.1.2 -- cookie-signature@1.0.5 -- debug@2.1.1 -- ms@0.6.2 -- depd@1.0.0 -- escape-html@1.0.1 -- etag@1.5.1 -- crc@3.2.1 -- finalhandler@0.3.3 -- fresh@0.2.4 -- media-typer@0.3.0 -- merge-descriptors@0.0.2 -- methods@1.1.1 -- on-finished@2.2.0 -- ee-first@1.1.0 -- parseurl@1.3.0 -- path-to-regexp@0.1.3 -- proxy-addr@1.0.6 -- forwarded@0.1.0 -- ipaddr.js@0.1.8 -- qs@2.3.3 -- range-parser@1.0.2 -- send@0.11.1 -- destroy@1.0.3 -- mime@1.2.11 -- ms@0.7.0 -- serve-static@1.8.1 -- type-is@1.5.7 -- mime-types@2.0.9 -- mime-db@1.7.0 -- utils-merge@1.0.0 -- vary@1.0.0 Now Let's try installing express, a popular web framework using global installation. C:\Nodejs WorkSpace npm install express - g Once npm completes the download, you can verify by looking at the content of userdirectory /npm/node modules. Or type the following command: C:\Nodejs WorkSpace npm ls -g Installing a module Installation of any module is as simple as typing the following command. C:\Nodejs WorkSpace npm install express Now you can use it in your js file as following: var express require('express'); Using package.json package.json is present in the root directoryt of any Node application/module and is used to define the properties of a package. Let's open package.json of express package present in C:\Nodejs Workspace\node modules\express\ { "name": "express", "description": "Fast, unopinionated, minimalist web framework", "version": "4.11.2",

"author": { "name": "TJ Holowaychuk", "email": "tj@vision-media.ca" }, "contributors": [ { "name": "Aaron Heckmann", "email": "aaron.heckmann github@gmail.com" }, { "name": "Ciaran Jessup", "email": "ciaranj@gmail.com" }, { "name": "Douglas Christopher Wilson", "email": "doug@somethingdoug.com" }, { "name": "Guillermo Rauch", "email": "rauchg@gmail.com" }, { "name": "Jonathan Ong", "email": "me@jongleberry.com" }, { "name": "Roman Shtylman", "email": "shtylman expressjs@gmail.com" }, { "name": "Young Jae Sim", "email": "hanul@hanul.me" } ], "license": "MIT", "repository": { "type": "git", "url": "https://github.com/strongloop/express" }, "homepage": "http://expressjs.com/", "keywords": [ "express", "framework", "sinatra", "web", "rest", "restful", "router", "app", "api" ], "dependencies": { "accepts": " 1.2.3", "content-disposition": "0.5.0", "cookie-signature": "1.0.5", "debug": " 2.1.1", "depd": " 1.0.0", "escape-html": "1.0.1", "etag": " 1.5.1", "finalhandler": "0.3.3", "fresh": "0.2.4", "media-typer": "0.3.0", "methods": " 1.1.1", "on-finished": " 2.2.0", "parseurl": " 1.3.0", "path-to-regexp": "0.1.3", "proxy-addr": " 1.0.6", "qs": "2.3.3", "range-parser": " 1.0.2", "send": "0.11.1", "serve-static": " 1.8.1", "type-is": " 1.5.6", "vary": " 1.0.0", "cookie": "0.1.2", "merge-descriptors": "0.0.2",

"utils-merge": "1.0.0" }, "devDependencies": { "after": "0.8.1", "ejs": "2.1.4", "istanbul": "0.3.5", "marked": "0.3.3", "mocha": " 2.1.0", "should": " 4.6.2", "supertest": " 0.15.0", "hjs": " 0.0.6", "body-parser": " 1.11.0", "connect-redis": " 2.2.0", "cookie-parser": " 1.3.3", "express-session": " 1.10.2", "jade": " 1.9.1", "method-override": " 2.3.1", "morgan": " 1.5.1", "multiparty": " 4.1.1", "vhost": " 3.0.0" }, "engines": { "node": " 0.10.0" }, "files": [ "LICENSE", "History.md", "Readme.md", "index.js", "lib/" ], "scripts": { "test": "mocha --require test/support/env --reporter spec --bail --check-leaks test/ test/acceptance/", "test-cov": "istanbul cover node modules/mocha/bin/ mocha -- --require test/support/env --reporter dot --check-leaks test/ test/acceptance/", "test-tap": "mocha --require test/support/env --reporter tap --check-leaks test/ test/acceptance/", "test-travis": "istanbul cover node modules/mocha/bin/ mocha --report lcovonly -- -require test/support/env --reporter spec --check-leaks test/ test/acceptance/" }, "gitHead": "63ab25579bda70b4927a179b580a9c580b6c7ada", "bugs": { "url": "https://github.com/strongloop/express/issues" }, " id": "express@4.11.2", " shasum": "8df3d5a9ac848585f00a0777601823faecd3b148", " from": "express@*", " npmVersion": "1.4.28", " npmUser": { "name": "dougwilson", "email": "doug@somethingdoug.com" }, "maintainers": [ { "name": "tjholowaychuk", "email": "tj@vision-media.ca" }, { "name": "jongleberry", "email": "jonathanrichardong@gmail.com" }, { "name": "shtylman", "email": "shtylman@gmail.com" }, { "name": "dougwilson", "email": "doug@somethingdoug.com" }, { "name": "aredridel", "email": "aredridel@nbtsc.org" }, {

"name": "strongloop", "email": "callback@strongloop.com" }, { "name": "rfeng", "email": "enjoyjava@gmail.com" } ], "dist": { "shasum": "8df3d5a9ac848585f00a0777601823faecd3b148", "tarball": 2.tgz" }, "directories": {}, " resolved": .2.tgz", "readme": "ERROR: No README data found!" } Attributes of Package.json name - name of the package version - version of the package description - description of the package homepage - homepage of the package author - author of the package contributors - name of the contributors to the package dependencies - list of dependencies. npm automatically installs all the dependencies mentioned here in the node module folder of the package. repository - repository type and url of the package main - entry point of the package keywords - keywords Uninstalling a module Use following command to uninstall a module. C:\Nodejs WorkSpace npm uninstall express Once npm uninstall the package, you can verify by looking at the content of userdirectory /npm/node modules. Or type the following command: C:\Nodejs WorkSpace npm ls Updating a module Update package.json and change the version of the dependency which to be updated and run the following command. C:\Nodejs WorkSpace npm update Search a module Search package name using npm. C:\Nodejs WorkSpace npm search express Create a module Creation of module requires package.json to be generated. Let's generate package.json using npm. C:\Nodejs WorkSpace npm init

This utility will walk you through creating a package.json file. It only covers the most common items, and tries to guess sane defaults. See 'npm help json' for definitive documentation on these fields and exactly what they do. Use 'npm install pkg --save' afterwards to install a package and save it as a dependency in the package.json file. Press C at any time to quit. name: (Nodejs WorkSpace) Once package.json is generated. Use following command to register yourself with npm repository site using a valid email address. C:\Nodejs WorkSpace npm adduser Now its time to publish your module: C:\Nodejs WorkSpace npm publish NODE.JS - CALLBACKS CONCEPT What is Callback? Callback is an asynchronous equivalent for a function. A callback function is called at the completion of a given task. Node makes heavy use of callbacks. All APIs of Node are written is such a way that they supports callbacks. For example, a function to read a file may start reading file and return the control to execution environment immidiately so that next instruction can be executed. Once file I/O is complete, it will call the callback function while passing the callback function, the content of the file as parameter. So there is no blocking or wait for File I/O. This makes Node.js highly scalable, as it can process high number of request without waiting for any function to return result. Blocking Code Example Create a txt file named test.txt in C:\ Nodejs WorkSpace TutorialsPoint.Com Create a js file named test.js in C:\ Nodejs WorkSpace var fs require("fs"); var data fs.readFileSync('test.txt'); console.log(data.toString()); console.log("Program Ended"); Now run the test.js to see the result: C:\Nodejs WorkSpace node test.js Verify the Output TutorialsPoint.Com Program Ended Non-Blocking Code Example Create a txt file named test.txt in C:\ Nodejs WorkSpace TutorialsPoint.Com Update test.js in C:\ Nodejs WorkSpace var fs require("fs"); fs.readFile('test.txt', function (err, data) { if (err) return console.error(err);

console.log(data.toString()); }); console.log("Program Ended"); Now run the test.js to see the result: C:\Nodejs WorkSpace node test.js Verify the Output Program Ended TutorialsPoint.Com Event Loop Overview Node js is a single threaded application but it support concurrency via concept of event and callbacks. As every API of Node js are asynchronous and being a single thread, it uses async function calls to maintain the concurrency. Node uses observer pattern. Node thread keeps an event loop and whenever any task get completed, it fires the corresponding event which signals the event listener function to get executed. Event Driven Programming Node.js uses Events heavily and it is also one of the reason why Node.js is pretty fast compared to other similar technologies. As soon as Node starts its server, it simply initiates its variables, delcares functions and then simply waits for event to occur. While Events seems similar to what callbacks are. The difference lies in the fact that callback functions are called when an asynchronous function returns its result where event handling works on the observer pattern. The functions which listens to events acts as observer. Whenever an event got fired, its listener function starts executing. Node.js has multiple in-built event. The primary actor is EventEmitter which can be imported using following syntax //import events module var events require('events'); //create an eventEmitter object var eventEmitter new events.EventEmitter(); Example Create a js file named test.js in C:\ Nodejs WorkSpace. File: test.js //import events module var events require('events'); //create an eventEmitter object var eventEmitter new events.EventEmitter(); //create a function connected which is to be executed //when 'connection' event occurs var connected function connected() { console.log('connection succesful.'); // fire the data received event eventEmitter.emit('data received.'); } // bind the connection event with the connected function eventEmitter.on('connection', connected); // bind the data received event with the anonymous function eventEmitter.on('data received', function(){ console.log('data received succesfully.'); }); // fire the connection event eventEmitter.emit('connection'); console.log("Program Ended.");

Now run the test.js to see the result: C:\Nodejs WorkSpace node test.js Verify the Output. Server has started connection succesful. data received succesfully. Program Ended. How Node Applications Work? In Node Application, any async function accepts a callback as a last parameter and the callback function accepts error as a first parameter. Let's revisit the previous example again. var fs require("fs"); fs.readFile('test.txt', function (err, data) { if (err){ console.log(err.stack); return; } console.log(data.toString()); }); console.log("Program Ended"); Here fs.readFile is a async function whose purpose is to read a file. If an error occur during read of file, then err object will contain the corresponding error else data will contain the contents of the file. readFile passes err and data to callback function after file read operation is complete. NODE.JS - EVENT EMITTER EventEmitter class lies in events module. It is accessibly via following syntax: //import events module var events require('events'); //create an eventEmitter object var eventEmitter new events.EventEmitter(); When an EventEmitter instance faces any error, it emits an 'error' event. When new listener is added, 'newListener' event is fired and when a listener is removed, 'removeListener' event is fired. EventEmitter provides multiple properties like on and emit. on property is used to bind a function with the event and emit is used to fire an event. Methods Sr. No. method Description 1 addListener event, listener Adds a listener to the end of the listeners array for the specified event. No checks are made to see if the listener has already been added. Multiple calls passing the same combination of event and listener will result in the listener being added multiple times. Returns emitter, so calls can be chained. 2 onevent, listener Adds a listener to the end of the listeners array for the specified event. No checks are made to see if the listener has already been added. Multiple calls passing the same combination of event and listener will result in the listener being added multiple times. Returns emitter, so calls can be chained. 3 onceevent, listener Adds a one time listener for the event. This listener is invoked only the next time the event is fired, after which it is removed. Returns emitter, so calls can be chained. 4 removeListener Remove a listener from the listener array for the specified event.

event, listener Caution: changes array indices in the listener array behind the listener. removeListener will remove, at most, one instance of a listener from the listener array. If any single listener has been added multiple times to the listener array for the specified event, then removeListener must be called multiple times to remove each instance. Returns emitter, so calls can be chained. 5 removeAllListeners [event] Removes all listeners, or those of the specified event. It's not a good idea to remove listeners that were added elsewhere in the code, especially when it's on an emitter that you didn't create e. g. socketsorfilestreams. Returns emitter, so calls can be chained. 6 setMaxListenersn By default EventEmitters will print a warning if more than 10 listeners are added for a particular event. This is a useful default which helps finding memory leaks. Obviously not all Emitters should be limited to 10. This function allows that to be increased. Set to zero for unlimited. 7 listenersevent Returns an array of listeners for the specified event. 8 emit event, [arg1], [arg2], [. . . ] Execute each of the listeners in order with the supplied arguments. Returns true if event had listeners, false otherwise. Class Methods Sr. No. method Description 1 listenerCountemitter, event Return the number of listeners for a given event. Events Sr. No. event name 1 newListener Parameters event String The event name Description This event is emitted any time a listener is added. When this event is triggered, the listener may not yet have been added to the array of listeners for the event. listener Function The event handler function 2 removeListener event String The event name listener Function The event handler function This event is emitted any time someone removes a listener. When this event is triggered, the listener may not yet have been removed from the array of listeners for the event.

Example Create a js file named test.js in C:\ Nodejs WorkSpace. File: test.js var events require('events'); var eventEmitter new events.EventEmitter(); //listener #1 var listner1 function listner1() { console.log('listner1 executed.'); } //listener #2 var listner2 function listner2() { console.log('listner2 executed.'); } // bind the connection event with the listner1 function eventEmitter.addListener('connection', listner1); // bind the connection event with the listner2 function eventEmitter.on('connection', listner2); var eventListeners Emitter,'connection'); console.log(eventListeners " Listner(s) listening to connection event"); // fire the connection event eventEmitter.emit('connection'); // remove the binding of listner1 function eventEmitter.removeListener('connection', listner1); console.log("Listner1 will not listen now."); // fire the connection event eventEmitter.emit('connection'); eventListeners Emitter,'connection'); console.log(eventListeners " Listner(s) listening to connection event"); console.log("Program Ended."); Now run the test.js to see the result: C:\Nodejs WorkSpace node test.js Verify the Output. Server has started 2 Listner(s) listening to connection event listner1 executed. listner2 executed. Listner1 will not listen now. listner2 executed. 1 Listner(s) listening to connection event Program Ended. NODE.JS - BUFFER MODULE buffer module can be used to create Buffer and SlowBuffer classes. Buffer module can be imported using following syntax. var buffer require("buffer") Buffer class Buffer class is a global class and can be accessed in application without importing buffer module. A Buffer is a kind of an array of integers and corresponds to a raw memory allocation outside the V8 heap. A Buffer cannot be resized.

Methods Sr. No. method 1 new Buffersize 2 new Bufferbuffer 3 new Bufferstr[, encoding] Parameters size Number Description Allocates a new buffer of size octets. Note, size must be no more than kMaxLength. Otherwise, a RangeError will be thrown here. buffer Buffer Copies the pass

Node.js is a web application framework built on Google Chrome's JavaScript EngineV8Engine. Its latest version is v0.10.36. Defintion of Node.js as put by its official documentation is as follows: Node.js is a platform built on Chrome's JavaScript runtime for easily building fast, scalable network applications. Node.js uses an event-driven .